This invention is directed to a new process to recover copper and other metallic elements from iron-containing copper smelter reverberatory slag without producing huge quantities of iron sulfate therefrom. Reverberatory slag from copper smelters is mainly composed of iron and aluminum silicates, having relatively low melting points, and copper and zinc. The copper and zinc values are usually present in the form of insoluble silicious material.
Such reverberatory slag has long been treated as a waste product and accumulated slag at smelter sites in various locations of the Western United States probably exceeds 200 million tons containing up to a million tons of copper and as much as 6 million tons of zinc. Several methods have been disclosed for leaching the slag, including those in U.S. Pat. Nos. 3,269,831; 3,273,997; 3,288,597 and 3,632,308. These utilize sulfuric acid to form copper sulfate, but produce large quantities of iron sulfate waste in addition to the copper obtained. The disposal of iron sulfate presents a serious problem since the quantities of iron sulfate produced from leaching operations and various other industrial processes exceeds market demands. Further, the large amount of sulfuric acid required for conventional processing of slag presents cost, equipment and environmental problems.
The recovery of copper from reverberatory slag by a method which avoids the use of large quantities of sulfuric acid and the formation of large quantities of iron sulfate therefrom is, therefore, highly desired.